Ok, my take on Rare Candy. Please try to follow.
As a rule of thumb, use it only on Legendaries. For a number of reasons, namely:
- they are hard to get
- most won't be returning so you won't get other chances of getting candy
- they're overpowered
- you have to walk 20 km for 1 candy.
Obviously, this depends on how you play, if you manage to raid and get bosses and if you like playing with Legendaries, but truth is, they make life (much) easier.
Rayquaza has the highest neutral DPS out of any pokes. You can basically solo almost everything (Tier 3) just with a team of maxed out Rayquazas (some people have it), including the mighty Jolteon. Although a great Dragonite is bulkier and can do much of the same, with less power. So I wouldn't recommend investing if you already have a Dragon squad.
Mewtwo is second on that list and Confusion/PsychoCut+Shadow Ball is the MVP in a number of matchups. Gengar, Alakazam, Machamp, Claydol, Jynx all kneel to King Mewtwo. He's the best against them all (just behind Kyogre on Claydoll). Then, he is a fantastic generalist and Focus Blast Mewtwo swipes through gyms with Blissey, Chansey, Snorlax and Tyranitar. He's that good. And he's Mewtwo. Safe investment and recommended.
Raikou is the most overpowered electric type with a fantastic moveset that allows you to hit hard and dodge with ease by using Thundershock+WildCharge. Zapdos follows closely behind with a worse moveset. They will be the overall best counters against the Lati-twins. I recommend Raikou.
Kyogre is the best water type out of all generations to come, this thing is a beast and a single waterfall hits like a freaking truck. Essential if you want to solo Claydol. Did you read the first sentence? Yeah, you won't get a better water type. Against Groudon, he matches a maxed L40 Gyarados at level 24. Yup, safe investment.
Groudon is crippled by ground's poor attacks but Solar Beam alone made him the top counter versus Kyogre with thunder. And if you have a team of Groudons, you can basically solo Jolteon while in your sleep. Not my priority as I have a Rhydon squad, but my weather boosted ones serve me good.
Then you have both fantastic fire types Moltres and Entei, which are left behind just because fire is not meta-relevant at the moment. They will be very useful for Registeel and Regirock and are fantastic counters to Jynx, one of them may be a good idea. If not, Flareon is awesome (just don't spend any rare candy on it!)
Lugia can solo Machamp on its own. And Sky Attack just got boosted, which means he can even do weather boosted Machamp now. 1vs1, no revives wasted... Also he's the most potion-efficient gym sweeper of the game. He makes life easier, I love my Lugia.
Ho-Oh is powerful but basically has shit moveset so I wouldn't touch him without any change.
Suicune is awesome outside of Pogo, Niantic just slaughtered him.
Bottom line: legendaries take your team to the next level, and they are the safest dump for your rare candies. Don't spend them on anything you can walk.
If you don't like Legendaries or can't catch them, think about saving the candy or using it on rare pokes you can't find any other way. Other great investments are obviously Chansey, Ralts (great attacker and Defender), Feebas (milotic is awesome and a brilliant defender), Beldum and other 5km-walking pokes. I wouldn't recommend using it on starters as you can just walk them and they nest, which means that if you go to certain places (check Silph Road) you can probably get all your candies in one afternoon.
2nd Non-nesting Rare 5-km walking Pokes
3rd Your fave poke just because you love it and yolo
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